There are a few companies that make a spray on tint product but you need to make sure everything is EXTREMELY CLEAN. Rustolium makes a pretty good one and its available at most auto stores. Im not sure what the laws look like in Ohio but I know here in Cali we have specific brightness regulations. If you plan on tinting your brake lamps I would suggest some High power LED replacement brake bulbs /edit/ on the 11+ WRX the brake lamps are LED already should be pleanty bright to shine through light tinting. Depending on how black you choose to go you may not be able to satisfy brightness requirements / edit/ I definitly recommend CREE reverse lamps.

only the wagon had led tail lights/brake lights. the sedan has regular bulbs. Only led light on the back of a sedan is if you have the wrx spoiler which has a led brake light which appears the OP has an sti wing so he has no leds that are stock. Just a little FYI fun fact.

I did mine with vht nite shades paint. First sand with 1000 grit, clean really well, clean again, spray light coats to desired darkness, spray clear coat the more the better, wet sand lightly with 1000+ sandpaper, buff and polish with compound. Ill post pics of mine if I can find or take any.

Honestly though I would recommend laminx pre cut tint overlays. They are nice and thick. Most importantly though they are easily reversible.